Conventionally, a permeable member is attached to electrical components for a vehicle, such as a lamp, pressure sensor and ECU (Electrical Control Unit), and to casings of electric appliances, such as a mobile-phone and camera. The permeable member ensures ventilation between the inside and outside of the casing and prevents the foreign objects from intruding into the casing. Attaching the permeable member to the casing enables a pressure change inside of the casing accompanying a temperature change to be alleviated, sounds to be transmitted between the inside and outside of the casing and a gas generated in the casing to be discharged to outside, while preventing water, dust and the like from intruding into the casing.
One example of such a permeable member is disclosed in JP2001-143524A. The permeable member 101 disclosed in JP2001-143524A is provided with a tubular support 103 wherein a permeable film 102 is arranged on its end face and with a protective cover 104 that has a bottom and is fitted into the support 103 so that the protective cover 104 covers the permeable film 102, as shown in FIG. 20. The permeable member 101 is fixed to a casing 105 so as to cover an opening 106 of the casing 105. In this case, when using the support 103 that has a smaller inside diameter than an outside diameter of the opening 106, the permeable member 101 can be fixed to the casing 105 using an elastic force generated by extension of the support 103. In this publication, an elastomer is exemplified as a material for the support 103.
For the purpose of preventing a permeable member from coming off from a casing, that is to say for the purpose of enhancing a pullout strength of the member, a large elastic modulus of the support is preferable. However, when the elastic modulus becomes excessively large, it becomes difficult to ensure the sealing property between the casing and the permeable member since the support can not follow the unevenness present on the surface of the opening. In order to enhance the pullout strength while the sealing property of the permeable member is maintained, a radial thickness of the support may be thickened more than the conventional thickness, or a ratio of the inside diameter of the support relative to the outside diameter of the opening may be smaller than a conventional ratio.
However, if the radial thickness of the support is set to be large, the size of the permeable member becomes large and it may affect packaging of the casing to which the permeable member is fixed. In particular, an influence on the electrical component, which is demanded to be downsized, is great. If the ratio of the inside diameter of the support relative to the outside diameter of the opening is set to be small, the size of the permeable member can be maintained but a permeable area of the permeable film that is attached to an end face of the support decreases, which affects the permeation characteristics. In addition, a deformation amount of the support for fixing it to the casing becomes large and thereby the permeable film supported by the support may be deformed.
It is an object of the present invention to provide a permeable member which can attain both a pullout strength and following property (sealing property) by including a support with a nonconventional constitution, and to provide a permeable casing and an electrical component, using the permeable member.